Electronic aerosol provision system

ABSTRACT

An aerosol provision system comprises a heating element for generating an aerosol from a source liquid and control circuitry for controlling a supply of electrical power from a power supply to the heating element. The control circuitry is configured to measure an indication of a derivative of an electrical characteristic of the heating element with respect to time. Based on the measured time derivative, the control circuitry is configured to determine whether or not a fault condition has arisen for the electronic aerosol provision system. The overall change in the electrical characteristic for the heating element caused by the localized heating may be small and so difficult to reliably identify, but the rate at which the change occurs can be expected to be relatively high, such that the time derivative of the local characteristic is a more reliable indicator of occurrence of the fault condition.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a National Phase entry of PCT Application No.PCT/GB2015/052290, filed Aug. 7, 2015, which claims priority from GBPatent Application No. 1415051.0, filed Aug. 26, 2014, which is herebyfully incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to electronic aerosol provision systemssuch as nicotine delivery systems (e.g. e-cigarettes and the like).

BACKGROUND

Electronic aerosol provision systems such as e-cigarettes generallycontain a reservoir of a source liquid containing a formulation,typically including nicotine, from which an aerosol is generated, e.g.through heat vaporization. An aerosol source for an aerosol provisionsystem may thus comprise a heater having a heating element adjacent to awick arranged to draw source liquid from the reservoir to the vicinityof the heating element. When a user inhales on the device, electricalpower is supplied to the heating element to vaporize source liquid fromthe wick to generate an aerosol for inhalation by the user. Such devicesare usually provided with one or more air inlet holes located away froma mouthpiece of the system. When a user sucks on the mouthpiece, air isdrawn in through the inlet holes and past the aerosol source. There is aflow path connecting between the aerosol source and an opening in themouthpiece so that air drawn past the aerosol source continues along theflow path to the mouthpiece opening, carrying some of the aerosol fromthe aerosol source with it. The aerosol-carrying air exits the aerosolprovision system through the mouthpiece opening for inhalation by theuser.

It is known in electronic aerosol provision systems to control the powersupplied to the heater's heating element to seek to provide a desiredperformance in terms of aerosol generation. For example, WO 2012/109371discloses a device in which a selection of an operating mode may dependon readings from temperature sensors inside the device. US 2014/0014126discloses a device in which the temperature of a heating element isdetermined from its resistance as it heats and cools to establish athermal time constant for the device. The power supplied to the heatingelement may then be adjusted based on the time constant. EP 2 316 286describes an electrically heated smoking system in which the temperatureof a heating element is determined from its resistance and power issupplied to the heating element in dependence on its temperature.Aerosol provision systems may also comprise other heaters, for exampleUS 2004/0149737 describes a device having an inductive heating systemfor removing condensates from electronic smoking systems in which thetemperatures of an arrangement of heaters are determined from theirrespective electrical resistances.

The present inventor has recognized a problem with existing aerosolprovision systems of the kind discussed above can arise if a portion ofthe wick adjacent a heating element becomes dry. This can happen, forexample, because the supply of source liquid to the wick may becomeunstable when the reservoir is becoming empty. The inventor hasrecognized in particular this condition can lead to rapid heating of theheating element in the vicinity of the dry portion of the wick. Theover-heating may be localized, but can also affect larger and moreextended sections of the heating element. Having regard to typicaloperating conditions, the over-heated section/hotspot might be expectedto quickly reach temperatures in the range 500 to 900° C. Not only doesthis degree of rapid heating potentially represent a risk of fire andburning for a user, radiant heat from the hotspot may damage componentswithin the aerosol provision system and may affect the evaporationprocess adversely. For example, heat from a hotspot may cause the sourceliquid and/or the generated aerosol to decompose, for example throughpyrolysis, which can potentially release unpleasant tasting substancesinto the air stream to be inhaled by a user. The heat from a hotspot mayalso ignite combustible vapor/air mixtures which in turn can increasethe temperature of the air stream to be inhaled by a user considerably.It is not only unstable wicking that can cause over-heating andhotspots. Over-heating can also be the result of too much electricalpower being provided to the heating element. If the heat flux exceeds acertain upper limit (typically around 1 W/mm²), nucleate boiling mayturn into film boiling, the latter boiling mechanism being much lesseffective, resulting in a sudden temperature rise of the heatingelement.

In view of the issues discussed above, there is a desire for methods andapparatus which are able to identify when there is rapid over-heating ofa heating element in an aerosol provision system, thereby allowingremedial action to be taken, for example by reducing power to theheating element, for example stopping the supply of power, and/orwarning a user.

SUMMARY

According to an aspect of certain embodiments, there is provided anelectronic aerosol provision system comprising: a heating element forgenerating an aerosol from a source liquid; and control circuitry forcontrolling a supply of electrical power from a power supply to theheating element, and wherein the control circuitry is further configuredto determine an indication of a derivative of an electricalcharacteristic of the heating element with respect to time; anddetermine whether or not a fault condition for the electronic aerosolprovision system has arisen based on the determined indication of thederivative of the electrical characteristic of the heating element withrespect to time.

According to another aspect of certain embodiments, there is provided amethod of operating an electronic aerosol provision system comprising aheating element for generating an aerosol from a source liquid andcontrol circuitry for controlling a supply of electrical power from apower supply to the heating element, wherein the method comprisesdetermining an indication of a derivative of an electricalcharacteristic of the heating element with respect to time; anddetermining whether or not a fault condition for the electronic aerosolprovision system has arisen based on the determined indication of thederivative of the electrical characteristic of the heating element withrespect to time.

The approaches described herein are not restricted to specificembodiments such as set out below, but include and contemplate anyappropriate combinations of features presented herein. For example, anelectronic aerosol provision system may be provided in accordance withthe approach described herein which includes any one or more of thevarious features described below as appropriate.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will now be described in detail by way of exampleonly with reference to the following drawings:

FIG. 1 is a schematic (exploded) diagram of an electronic aerosolprovision system such as an e-cigarette in accordance with someembodiments.

FIG. 2 is a schematic diagram of a main body portion of the e-cigaretteof FIG. 1 in accordance with some embodiments.

FIG. 3 is a schematic diagram of an aerosol source portion of thee-cigarette of FIG. 1 in accordance with some embodiments.

FIG. 4 is a schematic diagram showing certain aspects of one end of themain body portion of the e-cigarette of FIG. 1 in accordance with someembodiments.

FIG. 5 is a schematic flow diagram representing a mode of operation foran electronic aerosol provision system such as an e-cigarette inaccordance with some embodiments.

DETAILED DESCRIPTION

Aspects and features of certain examples and embodiments arediscussed/described herein. Some aspects and features of certainexamples and embodiments may be implemented conventionally and these arenot discussed/described in detail in the interests of brevity. It willthus be appreciated that aspects and features of apparatus and methodsdiscussed herein which are not described in detail may be implemented inaccordance with any conventional techniques for implementing suchaspects and features.

As described above, the present disclosure relates to an aerosolprovision system, such as an e-cigarette. Throughout the followingdescription the term “e-cigarette” is sometimes used but this term maybe used interchangeably with aerosol (vapor) provision system.

FIG. 1 is a schematic diagram of an aerosol/vapor provision system suchas an e-cigarette 10 in accordance with some embodiments (not to scale).The e-cigarette 10 has a generally cylindrical shape, extending along alongitudinal axis indicated by dashed line LA, and comprising two maincomponents, namely a body 20 and a cartomizer 30. The cartomizer 30includes an internal chamber containing a reservoir of a source liquidcomprising a liquid formulation from which an aerosol is to begenerated, for example containing nicotine, a heating element, and aliquid transport element (in this example a wicking element) fortransporting source liquid to the vicinity of the heating element. Thewicking element and the heating element may sometimes be collectivelyreferred to as an aerosol generator/aerosol source/aerosol formingmember/vaporizer/atomizer. The cartomizer 30 further includes amouthpiece 35 having an opening through which a user may inhale theaerosol from the aerosol generator. The source liquid may be of aconventional kind used in e-cigarettes, for example comprising 0-5%nicotine dissolved in a solvent comprising glycerol, water, or/andpropylene glycol. The source liquid may also comprise flavorings. Thereservoir for the source liquid may comprise a porous matrix or anyother structure within a housing for retaining the source liquid untilsuch time that it is required to be delivered to the aerosolgenerator/vaporizer.

As discussed further below, the body 20 includes a re-chargeable cell orbattery to provide power for the e-cigarette 10 and a circuit boardcomprising control circuitry for generally controlling the e-cigarette10. In use, when the heating element receives power from the battery, ascontrolled by the circuit board, the heating element vaporizes sourceliquid from the wicking element at a heating location in the vicinity ofthe heating element to generate an aerosol. The aerosol is inhaled by auser through the opening in the mouthpiece 35. During user inhalationthe aerosol is carried from the aerosol source to the mouthpiece 35opening along an air channel that connects between them.

In this particular example, the body 20 and cartomizer 30 are detachablefrom one another by separating in a direction parallel to thelongitudinal axis LA, as shown in FIG. 1, but are joined together whenthe device 10 is in use by a connection, indicated schematically in FIG.1 as 25A and 25B, to provide mechanical and electrical connectivitybetween the body 20 and the cartomizer 30. The electrical connector onthe body 20 that is used to connect to the cartomizer 30 also serves asa socket for connecting a charging device (not shown) when the body 20is detached from the cartomizer 30. The other end of the charging devicecan be plugged into an external power supply, for example a USB socket,to charge or to re-charge the cell/battery in the body 20 of thee-cigarette 10. In other implementations, a cable may be provided fordirect connection between the electrical connector on the body 20 andthe external power supply.

The e-cigarette 10 is provided with one or more holes (not shown inFIG. 1) for air inlet. These holes connect to an air running passagethrough the e-cigarette 10 to the mouthpiece 35. The air passageincludes a region around the aerosol source and a section comprising anair channel connecting from the aerosol source to the opening in themouthpiece 35.

When a user inhales through the mouthpiece 35, air is drawn into thisair passage through the one or more air inlet holes, which are suitablylocated on the outside of the e-cigarette 10. This airflow (or theresulting change in pressure) is detected by a pressure sensor that inturn activates the supply of electrical power from the battery to theheating element to vaporize a portion of the liquid source in thewicking element adjacent the heating element. Triggering the operationof the e-cigarette 10 in response to user inhalation may be implementedin accordance with conventional techniques. The airflow passes throughthe air passage and combines/mixes with the vapor in the region aroundthe aerosol source to generate the aerosol. The resulting combination ofairflow and vapor continues along the air channel connecting from theaerosol source to the mouthpiece 35 for inhalation by a user. Thecartomizer 30 may be detached from the body 20 and disposed of when thesupply of source liquid is exhausted (and replaced with anothercartomizer if so desired). Alternatively, the cartomizer 30 may berefillable.

Generally, the construction and operation of the e-cigarette 10 mayfollow established techniques in the field of aerosol provision systemsexcept where modified to provide functionality in accordance with themethods and apparatus described herein. It will therefore be appreciatedthe e-cigarette 10 shown in FIG. 1 is presented as a one exampleimplementation of an aerosol provision system according to the presentdisclosure, and various other implementations can be adopted in thecontext of other configurations of aerosol provision system. Forexample, in some embodiments, the cartomizer 30 may be provided as twoseparable components, namely a cartridge comprising the source liquidreservoir and mouthpiece (which can be replaced when the source liquidfrom the reservoir is exhausted), and a vaporizer/aerosol generatorcomprising a heating element (which is generally retained). As anotherexample, the charging facility and/or the heating element itself mayconnect to an additional or alternative power source, such as a carcigarette lighter socket. More generally, it will be appreciated thatembodiments of the disclosure described herein may be implemented inconjunction with any design of electronic aerosol provision system thatis based on an electronic heating element for vaporizing/aerosolizingsource liquid and the underlying operating principles and structuraldesign of other aspects of the aerosol provision system are notsignificant to the principles of operation in accordance with theembodiments described herein.

FIG. 2 is a schematic diagram of the body 20 of the e-cigarette 10 ofFIG. 1. FIG. 2 can generally be regarded as a cross-section in a planethrough the longitudinal axis LA of the e-cigarette 10. Note thatvarious components and details of the body 20, e.g. such as wiring andmore complex shaping, have been omitted from FIG. 2 for reasons ofclarity.

As shown in FIG. 2, the body 20 includes a battery or cell 210 forpowering the e-cigarette 10, as well as a circuit board 555 comprisingcontrol circuitry 550, in this example in the form of a chip, such as anapplication specific integrated circuit (ASIC) or microcontroller, forcontrolling the e-cigarette 10. The control circuitry 550 may bearranged alongside or at one end of the battery 210. The control circuit550 may be provided as a single element or a number of discreteelements. The control circuitry 550 is connected to a sensor unit 215 todetect an inhalation on mouthpiece 35 (or alternatively the sensor unit215 may be provided by the control circuitry 550 itself). In response tosuch a detection, the control circuitry 550 activates the supply ofpower from the battery or cell 210 to the heating element in thecartomizer 30 to vaporize source liquid and introduce an aerosol intothe airflow which is inhaled by a user. As noted above, this aspect ofthe operation may be conventional. However, in addition to beingconfigured to support the conventional operating aspects of thee-cigarette 10 in accordance with established techniques, the controlcircuit 550 is further configured in accordance with embodiments of thedisclosure to operate to determine whether or not a fault condition(corresponding to the occurrence of a hotspot/glowing/rapid over-heatingof the heating element) has arisen, as described further below. In thisregard, the body 20 of the aerosol provision system 10 in accordancewith this example implementation further comprises an indicator 560 toprovide a user with an indication (warning) of when a fault conditionhas arisen. The indicator 560 in this example comprises a light, forexample a light emitting diode, which is coupled to, and may be drivenby, the control circuitry 550. Other forms of indicator may be used, forexample a speaker for emitting a warning tone in response to a faultcondition being determined to have arisen.

The body 20 further includes a cap 225 to seal and protect the far(distal) end of the e-cigarette 10. There is an air inlet hole providedin or adjacent to the cap 225 to allow air to enter the body 20 and flowpast the sensor unit 215 when a user inhales on the mouthpiece 35. Thisairflow therefore allows the sensor unit 215 to respond to the userinhalation to trigger the control circuitry 550 to activate the aerosolgenerator element of the e-cigarette 10 (i.e. to supply electrical powerto the heating element).

At the opposite end of the body 20 from the cap 225 is the connector 25Bfor joining the body 20 to the cartomizer 30. The connector 25B providesmechanical and electrical connectivity between the body 20 and thecartomizer 30. The connector 25B includes a body connector 240, which ismetallic (silver-plated in some embodiments) to serve as one terminalfor electrical connection (positive or negative) to the cartomizer 30.The connector 25B further includes an electrical contact 250 to providea second terminal for electrical connection to the cartomizer 30 ofopposite polarity to the first terminal, namely body connector 240. Theelectrical contact 250 is mounted on a coil spring 255. When the body 20is attached to the cartomizer 30, the connector 25A on the cartomizer 30pushes against the electrical contact 250 in such a manner as tocompress the coil spring 255 in an axial direction, i.e. in a directionparallel to (co-aligned with) the longitudinal axis LA. In view of theresilient nature of the spring 255, this compression biases the spring255 to expand, which has the effect of pushing the electrical contact250 firmly against connector 25A, thereby helping to ensure goodelectrical connectivity between the body 20 and the cartomizer 30. Thebody connector 240 and the electrical contact 250 are separated by aspacer 260, which is made of a non-conductor (such as plastic) toprovide good insulation between the two electrical terminals. The spacer260 is shaped to assist with the mutual mechanical engagement ofconnectors 25A and 25B.

FIG. 3 is a schematic diagram of the cartomizer 30 of the e-cigarette 10of FIG. 1 in accordance with some embodiments. FIG. 3 can generally beregarded as a cross-section in a plane through the longitudinal axis LAof the e-cigarette. Note that various components and details of the body20, e.g. such as wiring and more complex shaping, have been omitted fromFIG. 3 for reasons of clarity.

The cartomizer 30 includes an aerosol source 365; 368 arranged in an airpassage 355 extending along the central (longitudinal) axis of thecartomizer 30 from the mouthpiece 35 to the connector 25A for joiningthe cartomizer 30 to the body 20. The aerosol source comprises aresistive heating element 365 adjacent a wicking element (liquidtransport element) 368 which is arranged to transport source liquid froma reservoir of source liquid 360 to the vicinity of the heating element365 for heating. The reservoir of source liquid 360 in this example isprovided around the air passage 335 and may be implemented, for example,by providing cotton or foam soaked in source liquid. Ends of the wickingelement 365 are in contact with the source liquid in the reservoir 360so that the liquid is drawn along the wicking element to locationsadjacent the extent of the heating element 365.

The general configuration of the wicking element 368 and the heatingelement 365 may follow conventional techniques. For example, in someimplementations the wicking element 368 and the heating element 365 maycomprise separate elements, e.g. a metal heating wire woundaround/wrapped over a cylindrical wick, the wick, for instance,consisting of a bundle, thread or yarn of glass fibers. In otherimplementations, the functionality of the wicking element 368 and theheating element 365 may be provided by a single element. That is to say,the heating element 365 itself may provide the wicking function. Thus,in various example implementations, the heating element 365/wickingelement 368 may comprise one or more of: a metal composite structure,such as porous sintered metal fiber media (Bekipor® ST) from Bakaert; ametal foam structure, e.g. of the kind available from MitsubishiMaterials; a multi-layer sintered metal wire mesh, or a foldedsingle-layer metal wire mesh, such as from Bopp; a metal braid; orglass-fiber or carbon-fiber tissue entwined with metal wires. The“metal” may be any metallic material having an appropriate electricresistivity to be used in connection/combination with a battery. Theresultant electric resistance of the heating element 365 will typicallybe in the range 0.5-5 Ohm. Values below 0.5 Ohm could be used but couldpotentially overstress the battery. The “metal” could, for example, be aNiCr alloy (e.g. NiCr8020) or a FeCrAl alloy (e.g. “Kanthal”) orstainless steel (e.g. AISI 304 or AISI 316).

As discussed further below, embodiments of the disclosure may rely onchanges in the resistance of a heating element with temperature toidentify the occurrence of fault conditions. Therefore, in accordancewith certain embodiments, the resistive heating element 365 is formedfrom a material with a relatively high temperature coefficient ofresistance. The temperature coefficient of some of the aforementionedmetals is relatively low (e.g. <0.0001 K⁻¹ for NiCr8020 and Kanthal).Stainless steel, however, has a higher temperature coefficient. Thus insome implementations stainless steel may be a preferred material for theheating element in the context of the present disclosure, but it will ofcourse be appreciated that other material could be used. The term“stainless steel” as used hereon may be interpreted according to theconventional terminology of metallurgy and comprises at least theSAE/AISI stainless steel series 100, 200, 300 and 400.

The heating element 365 is powered through lines 366 and 367, which arein turn connectable to opposing polarities (positive and negative, orvice versa) of the battery 210 via connector 25A and under the controlof the control circuitry 355 (the details of the wiring between thepower lines 366 and 367 and connector 25A are omitted from FIG. 3).

The connector 25A includes an inner electrode 375, which may besilver-plated or made of some other suitable metal. When the cartomizer30 is connected to the body 20, the inner electrode 375 contacts theelectrical contact 250 of the body 20 to provide a first electrical pathbetween the cartomizer 30 and the body 20. In particular, as theconnectors 25A and 25B are engaged, the inner electrode 375 pushesagainst the electrical contact 250 so as to compress the coil spring255, thereby helping to ensure good electrical contact between the innerelectrode 375 and the electrical contact 250.

The inner electrode 375 is surrounded by an insulating ring 372, whichmay be made of plastic, rubber, silicone, or any other suitablematerial. The insulating ring is surrounded by the cartomizer connector370, which may be silver-plated or made of some other suitable metal orconducting material. When the cartomizer 30 is connected to the body 20,the cartomizer connector 370 contacts the body connector 240 of the body20 to provide a second electrical path between the cartomizer 30 and thebody 20. In other words, the inner electrode 375 and the cartomizerconnector 370 serve as positive and negative terminals (or vice versa)for supplying power from the battery 210 in the body 20 to the heatingelement 365 in the cartomizer 30 via supply lines 366 and 367 under thecontrol of the control circuitry 550.

The cartomizer connector 370 is provided with two lugs or tabs 380A,380B, which extend in opposite directions away from the longitudinalaxis of the e-cigarette 10. These tabs are used to provide a bayonetfitting in conjunction with the body connector 240 for connecting thecartomizer 30 to the body 20. This bayonet fitting provides a secure androbust connection between the cartomizer 30 and the body 20, so that thecartomizer 30 and body 20 are held in a fixed position relative to oneanother, without wobble or flexing, and the likelihood of any accidentaldisconnection is very small. At the same time, the bayonet fittingprovides simple and rapid connection and disconnection by an insertionfollowed by a rotation for connection, and a rotation (in the reversedirection) followed by withdrawal for disconnection. It will beappreciated that other embodiments may use a different form ofconnection between the body 20 and the cartomizer 30, such as a snap fitor a screw connection.

FIG. 4 is a schematic diagram of certain details of the connector 25B atthe end of the body 20 in accordance with some embodiments (but omittingfor clarity most of the internal structure of the connector as shown inFIG. 2, such as spacer 260). In particular, FIG. 4 shows the externalhousing 201 of the body 20, which generally has the form of acylindrical tube. This external housing 201 may comprise, for example,an inner tube of metal with an outer covering of paper or similar.

The body connector 240 extends from this external housing 201 of thebody 20. The body connector as shown in FIG. 4 comprises two mainportions, a shaft portion 241 in the shape of a hollow cylindrical tube,which is sized to fit just inside the external housing 201 of the body20, and a lip portion 242 which is directed in a radially outwarddirection, away from the main longitudinal axis (LA) of the e-cigarette10. Surrounding the shaft portion 241 of the body connector 240, wherethe shaft portion 241 does not overlap with the external housing 201, isa collar or sleeve 290, which is again in a shape of a cylindrical tube.The collar 290 is retained between the lip portion 242 of the bodyconnector 240 and the external housing 201 of the body 20, whichtogether prevent movement of the collar 290 in an axial direction (i.e.parallel to axis LA). However, collar 290 is free to rotate around theshaft portion 241 (and hence also axis LA).

As mentioned above, the cap 225 is provided with an air inlet hole toallow air to flow past sensor 215 when a user inhales on the mouthpiece35. However, for this particular example aerosol provision system, themajority of air that enters the device 10 when a user inhales flowsthrough collar 290 and body connector 240 as indicated by the two arrowsin FIG. 4.

As noted above, there is a desire for schemes for determining theoccurrence of fault conditions in an aerosol provision system, and inparticular the occurrence of rapid over-heating of a heating elementincluding localized overheating (i.e. hotspots). Such overheating might,for example, be caused by a (possibly temporary) lack of source liquidfor heating in the vicinity of certain parts of a heating element.Likewise it might be caused by thermally overloading the heating elementwhen the heat flux exceeds a certain limit (e.g. around 1 W/mm²). It hasbeen previously proposed in the context of e-cigarette type devices todetermine the temperature of a heating element from its resistance, e.g.in US 2014/0014126 and EP 2 316 286. However, the inventor hasrecognized an approach such as this is relatively insensitive toidentifying the occurrence of rapid, possibly localized overheating,especially if materials with a relatively low temperature coefficient ofresistance (e.g. NiCr-alloys or Kanthal) are being used for the heatingelement. But even the higher temperature coefficient of stainless steelmay not provide the sensitivity required to determine localizedoverheating events (hotspots) using existing techniques. This is becausemeasuring the temperature of a heating element from its resistanceprovides an indication of an average temperature for the heating elementintegrated along its length. For example, with a heating element havinga length of 30 mm, and assuming negligible non-linear effects, it wouldnot be possible to distinguish between a uniform temperature increase of20° C. along the whole length of the heating element and a localizedtemperature increase of 200° along a 3 mm length of the heating elementfrom a measurement of the heating elements resistance. This means anacceptable increase in temperature for a larger part of the heatingelement can be indistinguishable from localized overheating which mightbe dangerous.

Thus, an aspect of aerosol provision system in accordance withembodiments of the present disclosure makes use of changes in a heatingelement's resistance with temperature to determine if a fault conditionhas arisen, but rather than seek to determine whether a fault conditionhas arisen based on the resistance for the heating element, approachesin accordance with certain embodiments of the present disclosure insteaddetermine whether a fault condition has arisen based on an observed time(t) derivative for the resistance (R) of the heating element (or acorrespondingly related electrical characteristic, such as conductance,current draw, power draw or voltage drop). For example, the timederivative may in some cases be a first derivative (i.e. dR/dt) and inother cases may be a second derivative (d²R/dt²).

FIG. 5 is a flow diagram schematically representing steps of a method ofoperating an electronic vapor provision system in accordance withcertain embodiments of the disclosure. Thus, in the context of theexample the e-cigarette represented in FIGS. 1 to 4, the controlcircuitry 550 is configured to provide functionality in accordance withthe method represented in FIG. 5.

Processing starts in S1 where it is assumed a user is in the process ofusing the electronic aerosol provision system 10 FIGS. 1 to 4.

In S2 the control circuitry 550 detects that the user has begun inhaling(i.e. the user has started sucking on the mouthpiece to draw air throughthe electronic aerosol provision system). This detection is based onsignals received from the sensor 215 and may be performed in accordancewith any generally conventional techniques.

In S3 the control circuitry 550 initiates the supply of electrical powerto the heating element 365 to begin vaporizing source liquid from thewicking element 368 to generate an aerosol for inhalation by the user.Again, this process may be performed in accordance with conventionaltechniques. In particular, the specific manner in which the electricalpower is supplied during normal operation (i.e. without a faultcondition been deemed to have occurred) may be chosen according to adesired performance in terms of the timing and extent of aerosolgeneration in accordance with conventional techniques. For example,electrical power may be supplied to the heating element for a timeperiod corresponding to the duration of a user's puff with variations inthe amount of power supplied (e.g. using pulse width modulation)throughout the user's puff to provide a desired level of aerosolgeneration in accordance with established techniques. S4 to S6 of FIG.5, which are discussed further below, are performed in an ongoingrepeating manner during the period in which power is supplied to theheating element and aerosol is generated.

In S4 the control circuitry 550 monitors the resistance R of the heatingelement. This may be achieved by measuring the resistance (or acorresponding electrical parameter such as conductance, current draw,power draw or voltage drop) of the heating element at a series ofdiscrete times, for example once every 10 ms. The process of measuringthe resistance of the heating element may be performed in accordancewith conventional resistance measurement techniques. That is to say, thecontrol circuitry 550 may comprise a resistance-measuring component thatis based on established techniques for measuring resistance (or acorresponding electrical parameter). In this regard theresistance-measuring component of the control circuitry 550 may becoupled to the heating element via the lines 366, 367 and the variouselements of the connector components 25A, 25B. In this regard, it willbe appreciated the control circuitry 550 may measure the combinedresistance of the heating element and the various components thatconnects the control circuitry 550 to the heating element 365. However,since the resistance of the other components in the resistance path isnot expected to change significantly with respect to time, this haslittle impact on measurements of the derivative of the resistance of theheating element with respect to time in accordance with embodiments ofthe disclosure described herein. It will further be appreciated thecurrent, power or voltage drop associated with the heating element (andhence its resistance) can also be determined from measurements of anelectrical characteristic (e.g. voltage or current/power draw) ofanother resistive element electrically coupled to the heating element,for example a power MOSFET, a shunt resistor, or even the battery itselfhaving regard to Kirchoff's voltage law.

In S5 a derivative of resistance R with respect to time t is determinedfrom a series of the resistance value established in S4 at differenttimes. That is to say, the control circuitry is configured to maintain arecord of previous values of R established according to the samplingperiod and to determine a time derivative of the established values. Forexample, the derivative may be a first derivative with respect to timeor a second derivative with respect to time. The derivative may bedetermined from the established values of R in accordance withconventional numerical processing techniques for determining gradientsfrom discrete measurements. For example, assuming a series of resistancemeasurements R₀, R₁, R₂, R₃ . . . R_(n−1), R_(n), R_(n+1) . . .established according to a regular sampling period p, an initiallydetermined indication of a first derivative at a time t_(n)(corresponding to the time of sample R_(n)) may simply be determinedaccording to:

dR/dt=(R _(n+1) −R _(n−1))/2p.

Similarly, an initially determined indication of a second derivative attime t_(n) (corresponding to the time of sample R_(n)) may simply bedetermined according to:

d ² R/dt ²=(R _(n+1) +R _(n−1)−2R _(n))/p ².

However, it will be appreciated there are various other well-establishedstatistical techniques for establishing a first derivative or a secondderivative from a series of samples. It will further be appreciated thatit is not necessary to determine an actual derivative in terms of ohmsper second, but rather an indication of the derivative is sufficient.For example, with a regular sampling period, there is no need to takeaccount of the actual time between samples as it will merely change theeffective units of the determined derivative(s). In this particularexample it is assumed the processing in Step S5 is based on thedetermination of a first derivative of resistance with respect to time(i.e. dR/dt).

In S6 the derivative established in S5 is compared with a thresholdvalue V. In effect the threshold value is an indication of the maximumrate of change of resistance that might be expected to occur withoutthere being any rapid overheating of the kind discussed above. If it isdetermined in S6 that the derivative established in S5 does not exceedthe pre-defined threshold value, processing follows the path marked “NO”back to S4 where processing continues as described above. However, if itis determined in S6 that the derivative established in S5 does exceedthe predefined threshold value, processing follows the path marked “YES”to S7.

In S7 it is determined that because a time derivative established in S5has been found to exceeded the pre-defined threshold value in thecomparison of S6, a fault condition is assumed to have occurred. Thisconclusion is based on the inventors' realization that whilst theresistance of the heating element is itself a relatively poor indicatorof rapid overheating, in particular for localized overheating (hotspots)developing on the heating element, the rate of change of resistance withrespect to time is a better indicator. This is because even though theoverall change in resistance may be similar for both a moderate increasein temperature across the whole heating element and a more significantlocalized overheating event, the rate at which the temperature changesin these two cases is different. In particular, localized overheating(thermal runaway) can be expected to occur more rapidly than uniformheating of the entire heating element.

A suitable threshold value to be used in S6 may be established throughcalculation, modeling or experiment. For example, a sample aerosolprovision system may be purposely driven into a condition that promoteshotspot development, and the derivative in resistance with respective totime may be measured as this happens. Likewise, the maximum derivativein resistance with respect to time during normal operation (i.e. withoutan overheating fault condition occurring) may be established. Thethreshold V may then be taken as a value somewhere between the maximumderivative in resistance seen during normal operation and the minimumderivative in resistance seen as a consequence of localizedoverheating/hotspot development, e.g. midway between these values.Aerosol provision systems of different designs will typically adoptdifferent threshold values.

Following the determination that a fault condition has occurred in S7,processing in this example proceeds to S8 in which the power supply tothe heating element is reduced, for example it may be switched offentirely. In this example the processing represented in FIG. 5 thenproceeds to S9 in which an indication of the occurrence of the faultcondition is raised by driving the indicator 560 to alert a user thatthe fault condition has occurred.

Further operation may vary according to the implementation at hand. Forexample, in some situations the aerosol provision system may in effectbecome “locked” and may not function again until a user has in effectreset the system, for example, by disconnecting and reattaching the body20 and the cartomizer 30 (in the expectation that this may be done torefill the reservoir 360 or replace a cartomizer 30 with a new one). Insome situations the aerosol provision system may only become “locked”(i.e. cease to function further) if there has been a number of faultcondition detection events detected within a given time period.

For optimum performance, the derivative of resistance with respect totime may be most sensitive to the development of a localized overheatingevent (hotspot) for the heating element when the temperature of theheating element is otherwise considered to be temporally steady. In thisregard, the processing represented in FIG. 5 may in some cases beimplemented only when the temperature of the heating element is expectedto remain in a steady state with the aerosol provision system operatingnormally. For instance, the processing may not be performed during apreheating phase, when the heating element is heated up from ambienttemperature to a vaporization/boiling temperature. Such preheating mayalso cause rapid heating of the heating element that could present in amanner similar to a fault condition. However in other situations theprocessing may be performed regardless of whether or not the temperatureof the heating element has stabilized. More generally, the method may beapplied during periods in which aerosol is being generated and/or duringa period in which electric power is being supplied to the heatingelement.

It will be appreciated various modifications to the apparatus andmethods described above may be implemented in accordance with certainembodiments of the disclosure. For example, in addition to determining aderivative of resistance with respect to time with a view toestablishing if a fault condition has arisen, the controller may also beconfigured to establish an effective average temperature for the heatingelement from the resistance measurements, for example to be used incontrolling a power supply to the heating element to provide a desireddegree and timing of aerosol generation in accordance with conventionaltechniques.

Furthermore, whilst the above-described examples have focused on theimplementations in which an indication of a time derivative forresistance is derived from discrete resistance measurements (i.e. ineffect using digital control circuitry), it will be appreciated anindication of the derivative of the resistance of the heating elementcan equally be established in the analogue domain using establishedanalogue electronics techniques, for example by using one or moreappropriately configured filters. Furthermore it will be appreciated theother steps presented in FIG. 5 could also be performed using analogue,rather than digital, electronic techniques. For example, functionalitycorresponding to S5 and S6 could be implemented by passing a signalindicative of the resistance of the heating element through a high-passfilter and comparing the output from the high-pass filter with athreshold level using a comparator.

As has already been noted above, it is not necessary to determine anactual derivative, e.g. in terms of ohms per second, but rather anindication of the derivative is sufficient, for example an indication ofwhether the derivative exceeds a particular threshold value consideredto correspond with a fault condition having arisen, e.g. based on whatis observed during empirical testing or modeling. For example, in oneimplementation the resistance of the heating element may be monitoredfor a given period of time during initial heater activation, for examplea period of time at the beginning of a user's puff. This period of timemay be considered a detection period and the device may be configured todetermine if the resistance of the heater changes by more than athreshold amount over a base-line resistance value during the detectionperiod. The base-line resistance value for normalizing subsequentmeasurements may correspond with a value of the heater resistancemeasured when the heater is cold, e.g. when a cartomizer is firstconnected to the body of the device or during periods between heateractivation. For the sake of providing a particular concrete example, inone implementation the detection period may have a duration of 400 msafter initial heater activation and a threshold value for the rate ofchange of resistance considered to indicate a fault condition may be anincrease of 14% over the baseline resistance measurement within this 400ms detection period (i.e. an increase of 0.14 in normalized resistance).Thus, if a measurement of resistance during the detection periodindicates an increase there is change in resistance which is greaterthan 14% of the baseline resistance value within the 400 ms detectionperiod, this indicates the rate of change of resistance is greater thanthe threshold for indicating a fault and the device may respondaccordingly.

Thus, there has been described an aerosol provision system, such as anelectronic cigarette, comprises a heating element for generating anaerosol from a source liquid and control circuitry for controlling asupply of electrical power from a power supply, such as a battery/cell,to the heating element. The control circuitry is configured to measurean indication of a derivative of an electrical characteristic of theheating element with respect to time, for example a first timederivative or a second time derivative of a resistance of the heatingelement (or a related parameter, such as conductance, current draw,power draw or voltage drop). Based on the measured time derivative, thecontrol circuitry is configured to determine whether or not a faultcondition, e.g. localized heating of the heating element, has arisen forthe electronic aerosol provision system. The overall change in theelectrical characteristic for the heating element caused by thelocalized heating may be small and so difficult to reliably identify,but the rate at which the change occurs can be expected to be relativelyhigh, which can mean the time derivative of the local characteristic ismore reliable indicator of the occurrence of the fault condition.

While the above described embodiments have in some respects focused onsome specific example aerosol provision systems, it will be appreciatedthe same principles can be applied for aerosol provision systems usingother technologies. That is to say, the specific manner in which variousaspects of the aerosol provision system which are not directly relevantto establishing whether a fault condition has arisen for a heatingelement in accordance with the approaches described herein is notsignificant to the principles underlying certain embodiments. Forexample, configurations based on the systems disclosed in US2011/0226236, could be used in other implementations.

In order to address various issues and advance the art, this disclosureshows by way of illustration various embodiments in which that which isclaimed may be practiced. The advantages and features of the disclosureare of a representative sample of embodiments only, and are notexhaustive and/or exclusive. They are presented only to assist inunderstanding and to teach the claimed invention(s). It is to beunderstood that advantages, embodiments, examples, functions, features,structures, and/or other aspects of the disclosure are not to beconsidered limitations on the disclosure as defined by the claims orlimitations on equivalents to the claims, and that other embodiments maybe utilized and modifications may be made without departing from thescope of the claims. Various embodiments may suitably comprise, consistof, or consist essentially of, various combinations of the disclosedelements, components, features, parts, steps, means, etc. other thanthose specifically described herein, and it will thus be appreciatedthat features of the dependent claims may be combined with features ofthe independent claims in combinations other than those explicitly setout in the claims. The disclosure may include other inventions notpresently claimed, but which may be claimed in future.

1. An electronic aerosol provision system comprising: a heating elementfor generating an aerosol from a source liquid; and control circuitryfor controlling a supply of electrical power from a power supply to theheating element, and wherein the control circuitry is further configuredto: determine an indication of a derivative of an electricalcharacteristic of the heating element with respect to time; anddetermine whether or not a fault condition for the electronic aerosolprovision system has arisen based on the determined indication of thederivative of the electrical characteristic of the heating element withrespect to time.
 2. The electronic aerosol provision system of claim 1,wherein the indication of the derivative of the electricalcharacteristic of the heating element with respect to time comprises anindication of a first derivative of the electrical characteristic of theheating element with respect to time.
 3. The electronic aerosolprovision system claim 1, wherein the indication of the derivative ofthe electrical characteristic of the heating element with respect totime comprises an indication of a second derivative of the electricalcharacteristic of the heating element with respect to time.
 4. Theaerosol provision system of claim 1, wherein the heating elementcomprises a resistive heating element.
 5. The aerosol provision systemof claim 4, wherein the resistive heating element comprises stainlesssteel.
 6. The electronic aerosol provision system of claim 1, whereinthe electrical characteristic of the heating element is based on one ormore characteristics selected from the group comprising: an electricalresistance associated with the heating element; an electricalconductance associated with the heating element; a current drawassociated with the heating element; a power draw associated with theheating element, a voltage drop associated with the heating element, anda voltage drop associated with another resistive element electricallycoupled to the heating element.
 7. The electronic aerosol provisionsystem of claim 1, wherein the control circuitry is further configuredto determine an indication of a temperature of the heating element frommeasurements of the electrical characteristic.
 8. The electronic aerosolprovision system of claim 1, wherein the fault condition is associatedwith a sudden rise in temperature of at least a portion of the heatingelement.
 9. The electronic aerosol provision system of claim 1, whereinthe fault condition is associated with occurrence of glowing of at leasta portion of the heating element.
 10. The electronic aerosol provisionsystem of claim 1, wherein the control circuitry is configured todetermine whether or not a fault condition for the electronic aerosolprovision system is arising or has arisen by comparing the indication ofthe derivative of the electrical characteristic of the heating elementwith respect to time with a predefined threshold value.
 11. Theelectronic aerosol provision system of claim 10, wherein the controlcircuitry is configured to determine the fault condition has arisen ifthe magnitude of the indication of the derivative of the electricalcharacteristic of the heating element with respect to time exceeds thepredefined threshold value.
 12. The electronic aerosol provision systemof claim 1, wherein the control circuitry is configured to determine theindication of the derivative of the electrical characteristic of theheating element with respect to time during a period in which thetemperature of the heating element is considered to be temporallysteady.
 13. The electronic aerosol provision system of claim 1, whereinthe control circuitry is configured to determine the indication of thederivative of the electrical characteristic of the heating element withrespect to time during a period in which aerosol is being generated bythe heating element.
 14. The electronic aerosol provision system ofclaim 1, wherein the control circuitry is configured to determine theindication of the derivative of the electrical characteristic of theheating element with respect to time during a period in which electricpower is being supplied to the heating element.
 15. The electronicaerosol provision system of claim 1, wherein the control circuitry isfurther configured to reduce the supply of power to the heating elementif it is determined the fault condition has arisen.
 16. The electronicaerosol provision system of claim 15, wherein the control circuitry isfurther configured to stop the supply of power to the heating element ifit is determined the fault condition has arisen.
 17. The electronicaerosol provision system of claim 1, wherein the control circuitry isfurther configured to activate a warning indicator if it is determinedthe fault condition has arisen.
 18. The aerosol provision system ofclaim 1, wherein the source liquid includes nicotine.
 19. The aerosolprovision system of claim 1, further comprising a reservoir of sourceliquid and a liquid transport element arranged to transport a portion ofthe source liquid to the vicinity of the heating element for heating togenerate the aerosol.
 20. The aerosol provision system of claim 1,further comprising the power supply in the form of a battery or cell.21. A method of operating an electronic aerosol provision systemcomprising a heating element for generating an aerosol from a sourceliquid and control circuitry for controlling a supply of electricalpower from a power supply to the heating element, wherein the methodcomprises: determining an indication of a derivative of an electricalcharacteristic of the heating element with respect to time; anddetermining whether or not a fault condition for the electronic aerosolprovision system has arisen based on the determined indication of thederivative of the electrical characteristic of the heating element withrespect to time.
 22. (canceled)
 23. (canceled)